The operation of dynamoelectric machinens, whether as motors or generators, is always accompanied by the generation of heat in the machine's varius components, including the stator. In order to prevent damage to the machine, such heat must be conducted away from the machine components; and so a variety of cooling schemes have been proposed for doing just that.
When a dynamoelectric machine is to operate in environments wherein a high power to weight ratio is desirable as, for example, in aircraft, the cooling means must be highly efficient and reject large quantities of heat in very short periods of time so that both the rotor and the stator may be made relatively small to minimize their weight.
One highly efficient means of rejecting heat from the stators of dynamoelectric machines may be employed in addition to conventional back iron cooling or, in many instances, without back iron cooling. It involves cooling the end turns, that is, that part of the stator winding that projects beyond the opposite sides of the stator core, by flowing a coolant through tubing in heat exchange relation with the end turns. Heat originating within the stator itself is conducted via the end turns to the coolant tubes whereat it is rejected and in many instances, such a system may eliminate any need for back iron cooling. Of course, if back iron cooling is employed, the system becomes all the more efficient in rejecting heat.
In any event, examples of this approach may be seen in U.S. Pat. No. 2,844,745 issued July 22, 1958 to Hamm and U.S. Pat. No. 3,109,947 issued Nov. 5, 1963 to Thompson et al. While the approaches illustrated in those patents are theoretically practical, the efficiency of heat removal can be increased if the heat transfer interfaces are held in contact with each other, particularly where the dynamoelectric machine must operate over a wide temperature range.
In particular, operation of a dynamoelectric machine over a wide temperature range will result in significant thermal growth of the various parts. Thus, is the coolant tubes of, for example, Hamm are expanded in the radial direction as the result of thermal growth, the heat transfer interface may become unbonded or permanently deformed. As the end turns begin to cool down for any of a variety of reasons, they may pull away from the coolant conduit and good heat exchange contact will be lost. As a result, the cooling efficiency of the system becomes diminished.
Furthermore, the relative movement between the end turns and the coolant conduit as a result of thermal growth can result in so-called "fretting" at the interface between the two components. Such fretting may wear through the insulating varnish or the like applied to the end turns. The problem is particularly severe where the conduits are formed of metal since fretting could result in the conduit's coming in contact with exposed conductors where the insulation on the end turns has worn away as a result of substantial fretting. This, of course, will result in an electrical short circuit of the dynamoelectric machine. If the conduits are formed of elastomer, excessive heat can cause deterioration thereof.
The present invention is directed to overcoming one or more of the above problems.